The present invention relates to a method for manufacturing a lithographic printing plate coated with at least physical development nuclei and a silver halide emulsion layer on an aluminum plate.
A lithographic printing plate which can utilize a transferred silver image obtained by the silver complex diffusion transfer reversal process (DTR process) as ink receptive portions has been known. A typical lithographic printing plate of this type is the one having an undercoat layer, a silver halide emulsion layer and a physical development nuclei layer on a support (such as a paper base coated with polyethylene resin and a poly(ethylene terephthalate) film base) in this order, and described, for example, in U.S. Pat. No. 3,721,559, No. 3,490,905, No. 3,385,701, No. 3,814,603, No. 3,454,398, No. 3,764,323, No. 3,099,209, No. 5,281,509, No. 5,641,605, JP-B-44-27242, JP-B-48-30562, JP-A-53-9603, JP-A-53-21602, JP-A-54-103104 and JP-A-56-9750.
The above-described lithographic printing plate has physical development nuclei on the surface of silver halide emulsion layer using gelatin as a binder, and exposed silver halide causes a chemical development by the DTR development to become black silver forming a hydrophilic non-image part which is mainly composed of gelatin. In contrast, unexposed silver halide is converted to silver salt complex by a silver salt complexing agent in a developer and diffuses to a physical development nuclei layer in the surface, where metal silver deposits on the physical development nuclei by a physical development to form an ink accepting silver image part.
On the other hand, a lithographic printing plate to which the present invention is directed (hereinafter referred to an aluminum printing plate) is the one which has physical development nuclei on a grained and anodized aluminum support, and further a silver halide emulsion layer thereon. Such aluminum printing plate is described, for example, in U.S. Pat. No. 5,427,889, No. 5,645,972, No. 5,853,950, No. 5,902,719, JP-A-57-118244, JP-A-57-158844, JP-A-63-260491, JP-A-3-116151, JP-A-5-216236 and JP-A-6-81194. This lithographic printing plate is subjected to the DTR development, then the silver halide emulsion layer is washed off with water to obtain a printing plate.
In more detail, metal silver deposits on the physical development nuclei by the DTR development to form a silver image part, which is exposed on an aluminum support by removing the silver halide emulsion layer after washing with water. At the same time, the anodized aluminum surface itself is exposed as a non-image part.
To the exposed silver image part and non-image part, a treatment, so called gumming, is applied, where a finishing solution containing a protective colloid such as gum arabic, dextrin, carboxymethyl-cellulose, polystyrene-sulfonic acid is coated for protecting them. This finishing solution is also called as a fixing solution or a finishing solution, containing a compound which makes the silver image part lipophilic (for example, a nitrogen-containing heterocyclic compound having a mercapto group or a thion group).
A typical process for manufacturing an aluminum lithographic printing plate comprises a process to produce an aluminum support by applying surface treatments such as graining and anodizing, a process for coating a liquid containing physical development nuclei on an aluminum support and a process for coating a silver halide emulsion layer. An aluminum lithographic printing plate produced by such manufacturing processes had a problem that a fine line image not wider than about 100 xcexcm does not reproduced on print. This is considered to be caused by a poor adhesion between the aluminum support and the physical development nuclei. Furthermore, the above-described aluminum printing plate had another problem that a spot-like defect tends to occur in the silver image part.
With regard to a method for manufacturing an aluminum lithographic printing plate, a method to give the physical development nuclei to an aluminum plate in the stage of surface treatment for an aluminum plate had also been proposed, and described, for example, in JP-A-6-301212, JP-A-7-56343, JP-A-7-64291 and JP-A-7-110578. However, no method has been put to a practical use until now because of problems such as an insufficient stability and a complicated facilities.
Accordingly, an object of the present invention is to provide a method for manufacturing an aluminum printing plate which is superior in a fine line reproduction and has no occurrence of the spot-like defect in the silver image.
The above-described object of the present invention was basically attained by a method for manufacturing a lithographic printing plate, wherein an aluminum plate subjected to at least graining treatment and anodizing treatment was rinsed with water, then coated with a liquid containing physical development nuclei in a wet state of the surface of the aluminum plate, and subsequently coated with a silver halide emulsion layer.